The present disclosure relates to a semiconductor integrated circuit, a current control method, an AD converter, a solid-state imaging device, and an electronic system. In particular, the present disclosure relates to a semiconductor integrated circuit, a current control method, an AD converter, a solid-state imaging device, and an electronic system that are capable of reliably reducing influence of an IR drop without an increase in the circuit size.
A current mirror circuit enables easy duplication of an output current, and thus is widely used when a large number of current sources are necessary. For a semiconductor integrated circuit including a current mirror circuit, a DA conversion circuit (DAC: Digital Analog Converter) using a current source is provided as illustrated in FIG. 1, for example.
In a DA conversion circuit in FIG. 1, a current mirror circuit is constituted by a first current source to a sixth current source that include a PMOS transistor individually connected to a power source line 11 and a bias line 12, and a bias block that includes a PMOS transistor through which a reference current Iref flows. In the DA conversion circuit in FIG. 1, a current value of each of currents I1 to I6 flowing through each current source is determined by the difference between a power source voltage and a bias voltage. That is to say, the current value is determined by a gate-source voltage Vgs of each of the PMOS transistors.
In a DA conversion circuit of this kind, an IR drop might occur on the power source line 11. Here, an IR drop is a voltage drop of the IR product that occurs on a power source line when a current abruptly increases. When an IR drop occurs, a voltage Vgs at each current source varies, and thus reduction in the influence of an IR drop is demanded.
In order to reduce the influence of such an IR drop, it is thought that the power source line 11 is strengthened. However, in order to strengthen the power source line 11, it is necessary to thicken the power source line 11, and thus the circuit size increases as a result.
Also, Japanese Unexamined Patent Application Publication No. 7-240690 has been disclosed as a technique for reducing the influence of an IR drop without increasing the circuit size. In Japanese Unexamined Patent Application Publication No. 7-240690, adjacently to a PMOS transistor of each current source included in a DA conversion circuit, a PMOS transistor is disposed in order to give a certain bias between the gate and the source thereof so that an output current from the PMOS transistor of each current source is kept at constant regardless of voltage variations.